Polyurethanes obtained from isocyanate terminated prepolymers prepared by reacting aromatic diisocyantes with polyethers or polyesters are subject to deterioration when exposed to ultraviolet light or nitrogen oxide acid fumes. This deterioration is manifested by a discoloration of the polyurethane, usually yellow to brown. It is also particularly apparent in films prepared from polyether based polyurethanes chain extended with water. This discoloration is also noticed in polyurethanes prepared from polyesters, as well as in shaped articles such as fibers.
The discoloration due to ultraviolet light can be reduced by the addition to the polyurethane of an ultraviolet absorber; however, the ultraviolet absorber has little or no effect in protecting the polymer against nitrogen oxide acid fumes. The addition of a commonly used hindered phenol antioxidant will serve to reduce the deterioration due to nitrogen oxides; however, there is little to no effect in reducing ultraviolet light degradation. Combinations of ultraviolet absorber and antioxidant can and have been used successfully. Note U.S. Pat. No. 3,379,675, Jensen et al, wherein a combination of 2,2'-(o-hydroxyphenyl)benzotriazole and 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene is added to a polyether based spandex fiber. The combination is reported to produce a synergistic effect which is greater than that expected from the simple additive effects of the two types of stabilizers used separately. The above phenolic compound and 1,2,4,5-tertramethyl-3,6-bis(3,5-di-t-butyl-4-hydroxybenzyl) benzene are reported to stabilize polyether based spandex fibers against deterioration due to acid fumes; see U.S. Pat. No. 3,395,114, Smith.
The present invention represents the culmination of a long series of investigations conducted largely by the inventors directed to overcoming the inherent problems of ultraviolet and nitrogen oxide degradation of polyurethane polymers obtained from isocyanate prepolymers prepared by reacting polyethers or polyesters with aromatic diisocyanates.
Accordingly, it is the primary object of the present invention to provide a polyurethane polymer stabilized against the degradative effects of ultraviolet light and nitrogen oxides.
Another object of the invention is to provide a process for avoiding the deterioration of polyurethane polymers.
Generally then, it is an object of this invention to provide polyurethane polymers which are stable against ultraviolet and nitrogen oxide deterioration.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be realized by practice of the invention, the objects and advantages being realized and attained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.